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Jae-Yong Kwon, Woohyun Jung, Sangsu Lee, October 2024
KRISS has introduced a 6-axis industrial robot into an antenna measurement system. This allows for various measurement applications and the continuous development of additional ones. Among these measurement applications, representative functions such as antenna gain measurement, material characteristics measurement, 3D field scanning, and RCS measurement are continuously being improved. The validity of the technology is discussed by comparing its results with measurements taken in a fully anechoic chamber.
Fabian T. Bette, Thomas M. Gemmer, Severin von Wnuck-Lipinski, Hendrik Bartko, Benoit Derat, Simon Otto, Maren Willemsen, Wilhelm Keusgen, October 2024
To verify the proper working of a Reconfigurable Intelligent Surface (RIS), similar to antenna radiation patterns, the RIS reflection pattern has been established as key performance indicator. To overcome the necessity of a bistatic RIS qualification setup, where two antennas at different positions are used, this paper presents a novel measurement approach to obtain the RIS reflection pattern based on a monostatic indirect Far-Field (FF) Compact Antenna Test Range (CATR) setup. Due to the monostatic principle, only one antenna, which is used for transmission and reception, is required. Subsequently, the mono- static reflection patterns are transformed into bistatic reflection patterns by applying different Monostatic to Bistatic Equivalence Theorems (MBETs) known from radar-cross-section theory. With that, the required setup can be simplified in terms of mechanical complexity, setup footprint and the number of measurement scenarios, since incident and reflection angle correspond in the monostatic case. This paper analyzes three different MBETs, namely Kell, Crispin/Siegel and Falconer, with respect to their suitability for RIS reflection pattern measurements. Moreover, a monostatic CATR test environment is presented and two metal plate based RIS calibration approaches are introduced. This novel monostatic RIS measurement approach is validated with simulation and measurement data of two mmWave fixed beam RISs. Both of them are reflecting an impinging signal from broadside (θ = 0°) direction into 47° at a center frequency of 27GHz. The results prove the suitability of this approach.
Donald P. Hillard, Michael S. Emire, Michael D. Safty, Richard W. Soard, Gary Salvail, Robert C. Simpson, October 2024
This paper presents research validating the conductive resonant sphere creeping wave phase dilation discovered in high-resolution imaging presented at the 2023 Antenna Measurement and Techniques Association (AMTA), which focused on using a small resonant sphere as a test probe for assessing Radar Cross Section measurement accuracy [1]. The associated analysis uncovered a discrepancy in the creeping wave Standard Model physical pathlength around the sphere having less phase than required for resonance. This paper presents a new creeping wave phase dilation model resolving the phase difference and validating results with computational electromagnetic field predictions.
Larger low-observable targets are being mounted onto RCS pylons. In many cases not only Azimuth rotation of the target, but a degree of movement in elevation is desired. This requires in many cases a large number of positioning cables to run from the base of the pylon to the tip where the rotator is placed. At the same time the low-observable qualities of the target call for pylon ogives with higher ratios to minimize the background RCS of the pylon that supports the target. The higher ratios call for very thin structures that cannot handle the weight of the rotator or have not enough space for the control and power cable to be fed to the rotator. A way of solving this problem is to have a variable ratio pylon, where the ogive at the tip is different from the ogive on the main body of the pylon. To analyze these pylons a higher-order basis-function method of moments (HOBFMoM) approach has been used in the past [1]. To conform the quadrilateral flat patches to the round geometry of the pylon, patches smaller than 0.3λ were used. While this was still an advantage over the typical 0.1to 0.05λ patches it placed limits on the highest frequencies that could be analyzed give the available computational resources. In this paper the authors present an approach to the meshing of the structure that allows for computing the monostatic RCS at frequencies in the x-band for a 2.4 m tall pylon. In addition, the effects of the non- physical absorber terminations are further analyzed.
Songyi Yen, Ljubodrag B. Boskovic, Dejan S. Filipovic, October 2024
A low-cost, custom radar cross-section (RCS) range is designed and built to measure the RCS of wideband linear and circular retrodirective arrays over a ground plane and good accuracy over 1-4 GHz is demonstrated. The only test equipment needed is a vector network analyzer (VNA). The 3.66 m × 1.22 m ground plane is constructed from a thin aluminum foil covering a frame constructed out of plywood and foam panels with wideband probe and wideband arrays inset into the ground plane. Excellent agreement with theoretical and simulated results is demonstrated. Additionally, the measurements validate a previously proposed method for the synthesis of the antenna component of the RCS using only the scattering parameters and embedded element patterns. Extension of this synthesis method into the measurements for the case when no beamforming network is available is demonstrated as well. Time-domain RCS measurements also agree well with theoretical and simulated data, which are used to illustrate the physics of linear Van Atta arrays.
At the Boeing 9-77 Range, we have used various dielectric strings and fishing ropes for target support. An advantage of a string-system is that when not at broadside to the incident wave, the strings would give rise to the least interference to the object being measured. A good example is a 60-ft long rod lifted from ground by the upper turntable (UTT) to the quiet-zone center, rotated horizontally and being measured. [1-2]
For the long rod with abruptly terminated ends, there is often a ringing, called the Gibbs phenomenon, which modulates the responses at both ends. Yet, for a 40-ft long vertical metal cylinder supported by a rope through its center, it was curious that the ringing did not show up. By reviewing the metal-dielectric interference, we now realized that the dielectric rope must have contributed an opposite effect such that the ringing ceased. These results are described and discussed. [3-4]
Papa Ousmane Leye, Daria Kulikova, Ming Dong, Chaouki Kasmi, Felix Vega, Islem Yahi, October 2024
Measuring radar cross-section (RCS) in high-noise environments remains a challenge. This paper presents an advanced signal processing framework that uses statistical dimensionality reduction to effectively separate the signal of interest from environmental noise. The proposed technique consists of two main steps. First, background subtraction and a gating technique are used to preprocess the measured data, separating and extracting the target’s reflectivity distribution from unwanted room contributions. Then, principal component analysis (PCA) is employed to analyze the target’s scattering image and localize its main scattering centers. To validate the proposed algorithm, a perfectly electrically conductive (PEC) scaled UAV model is manufactured and tested. The analysis of the experimental results demonstrates that the suggested technique effectively removes background and clutter, providing reliable RCS measurements in noisy environments.
Papa Ousmane Leye, Adamo Banelli, Shaikha Aldhaheri, Chaouki Kasmi, Felix Vega, Islem Yahi, October 2023
The purpose of radar cross-section (RCS)
measurement is to determine the amount of scattering that
occurs when the radar signal illuminates the target. It is
generally performed to prove a design concept. RCS
measurement chamber requires a good signal-to-noise ratio
during the measurement. When the measurement is
performed in a non-controlled environment, coherent
background subtraction associated with time gating is
commonly used to improve the quality of the RCS data.
Although these techniques are usually effective, residual
clutter and background level still need to be removed to
accurately characterize the target’s RCS in highly cluttered
environments, such as semi-anechoic chambers. In this
paper, a four-step post-processing technique is presented.
In addition to the vector background subtraction and timegating
techniques implemented in our previous work, a
statistical algorithm called Principal Component Analysis
(PCA) is applied to the ISAR image of the target. It is an
extension of the PCA technique to RCS measurement. It is
shown that residual background and clutter can be reduced
by the statistical filtering method through eigenvalue
decomposition of the RCS data. The technique is presented
and evaluated through measurement of the RCS of a
dihedral corner reflector at the X-band in the semi-anechoic
chamber of the Directed Energy Research Center.
Papa Ousmane Leye, Adamo Banelli, Shaikha Aldhaheri, Chaouki Kasmi, Felix Vega, Islem Yahi, October 2023
The purpose of radar cross-section (RCS)
measurement is to determine the amount of scattering that
occurs when the radar signal illuminates the target. It is
generally performed to prove a design concept. RCS
measurement chamber requires a good signal-to-noise ratio
during the measurement. When the measurement is
performed in a non-controlled environment, coherent
background subtraction associated with time gating is
commonly used to improve the quality of the RCS data.
Although these techniques are usually effective, residual
clutter and background level still need to be removed to
accurately characterize the target’s RCS in highly cluttered
environments, such as semi-anechoic chambers. In this
paper, a four-step post-processing technique is presented.
In addition to the vector background subtraction and timegating
techniques implemented in our previous work, a
statistical algorithm called Principal Component Analysis
(PCA) is applied to the ISAR image of the target. It is an
extension of the PCA technique to RCS measurement. It is
shown that residual background and clutter can be reduced
by the statistical filtering method through eigenvalue
decomposition of the RCS data. The technique is presented
and evaluated through measurement of the RCS of a
dihedral corner reflector at the X-band in the semi-anechoic
chamber of the Directed Energy Research Center.
The use of squat cylinders as both primary and
secondary calibration targets is commonplace within the radar
cross section (RCS) measurement community. Secondary
calibrations have become a best practice activity for ranges
seeking or maintaining certification. The calibration process, often
referred to by the measurement community as a “Dual-Cal,” uses
two squat cylinders of similar but unequal dimensions that provide
range operators with a broadband calibration vector and a
measurement uncertainty metric important to range certification.
Despite their popularity, the need to ensure resonance scattering
occurs below the desired measurement band results in physically
large cylinders at UHF. In addition, the need to access the test zone
for separate cylinder measurements may add substantial time to
the calibration process and require specialized equipment,
especially for large ranges.
In response to these issues, a 22.5-degree right dihedral has been
inserted into a squat cylinder form factor, creating a primary and
secondary calibration target within one body, each separated in
azimuth by 180 degrees. This two-target calibration device
removes the need to access the target zone twice and mitigates
errors associated with separate mounting schemes. The cylinder
aspect, now truncated by the imposition of a dihedral, has 50%
extended lower frequency coverage at UHF due to oblique edge
scattering at vertical polarization. At horizontal polarization, the
dihedral interruption of the cylinder creeping wave reduces its
contribution for ka<4. The dihedral aspect provides a full
polarimetric calibration, resulting in co-equal frequency responses
for each polarization in the high frequency limit. The design
parameters of the squat cylinder-dihedral device, its computed
full-wave frequency response, and relevant scattering features are
discussed.
In a compact range when the antenna is used
for both transmitting and receiving in a monostatic
fashion, the wave packet senses everything within its
view. An extended long object usually gives rise to a
bright reflection (glint) when viewed near its surface
normal. To take advantage of this phenomenon, a
discrete Fourier transform (DFT) on RCS measurements
would yield a spectrum of incident wave
distribution along that object, provided the scattering
property is uniform along its length. Compared with
traditional field-probes which translate a sphere across
the test zone in horizontal and vertical directions, this
new method extends out from the usual quiet zone, and
is faster and less interfering to the field being probed.
Inspired by this idea, the progression to practical
innovation is discussed.
Gil Yemini, Stefano Sensani, Andrea Giacomini, Lars Foged, Marcel Boumans, Matan Kahanov, Maria Baskin, Ilan Kaplon, October 2023
A new compact range for RCS measurements has
been installed and qualified by Orbit/FR Engineering Ltd. MVG.
It has a Quiet Zone of 3m diameter, 3m length and operates from
0.7 to 50 GHz, with a feed carousel that allows for fully
automated feed change. The RF design is not intended for
antenna measurements in its current configuration, but mainly
dedicated to RCS. The operational frequency band is split into
three sub-bands: each of the lower two bands have a monostatic
operated dual polarized feed, while the higher band has a quasimonostatic
operated feed configuration with two dual polarized
feeds. Pulsed Tx/Rx modules are directly integrated into the feed
assembly. Also, the RF band switching equipment, as well as the
network analyzer, are integrated in the feed carousel, so that
there are no flexing cables or any other relative movement of RF
components when the relevant feed is moved into the focus.
Together with tight temperature control, this leads to the best
possible RF stability. Since all measurements are time gated,
there is no need for an absorber baffle wall to prevent feed direct
leakage into the quiet zone. Thus, all feeds are mounted on a
clean absorber disk without any absorber blockage and
unwanted primary pattern distortion down to a conical angle of
90deg. This allows to obtain an exceptionally good QZ
performance even at the lowest frequencies, with an outstanding
comparison with the predictions based on Physical Optics.
The paper will describe the range design fundamentals, the feed
carousel concept and the relevant RF instrumentation. The Quiet
Zone performance evaluated by field probing with a Shorted
Antenna located in the Quiet Zone will be extensively presented,
demonstrating full compliance with the specifications.
Gil Yemini, Stefano Sensani, Andrea Giacomini, Lars Foged, Marcel Boumans, Matan Kahanov, Maria Baskin, Ilan Kaplon, October 2023
A new compact range for RCS measurements has been
qualified. It has a quiet zone of 3m diameter, 3m length and
operates from 0.7 to 50 GHz. The range is oriented for RCS
measurements, whereas antenna measurements are not foreseen.
All RF equipment is integrated close to the feeds with highly
integrated pulsed Tx/Rx-modules. Therefore, classical field
probing by moving a probe antenna along a linear slide would
require significant modification of the RF system. If one measures
the RCS of a target on the linear slide, it is difficult to distinguish
the target down range reflection from the reflection of the linear
slide structure. A long stand-off between target and slide is not
practical for mechanical reasons in regard to accuracy
requirements at 50 GHz. More important, simply measuring a
reflective plate will not give any cross-polarization information. A
more advanced target is created by using an antenna with a short
circuit after an RF cable to locate the reflection of the short well
behind the scanner in down range. In addition, the antenna
receives only nominal quiet zone co-polarization, consequently,
only reflects co-polarization from the short, and the feed receives
the compact range induced cross-polarization at the feed (oneway).
The method has shown to be extremely effective. More
important, it uses the RF instrumentation and RCS measurement
methods as designed for regular operation without any
modification, thus is the most realistic system level quality
representation of the quiet zone, can be repeated at any time
without elaborate range reconfiguration requirements and can
serve as part of the commissioned RF system performance
qualification.
The paper will present the quiet zone field probe test setup, a
calculation of antenna and RF cable requirements, an analysis of
the down range profile of scanner and reflective antenna and field
probing results.
Jon Kelley, Kurt Norris, Brian Mackie-Mason, Brody Barton, David Chamulak, Scott Schaeffer, Mark Martin, Kendall Crouch, Clifton Courtney, Ali Yilmaz, October 2023
—Cylindrical hubs with fan blades are inserted
into a pipe inside a modified camera box—a recently
introduced structure intended to host differently-shaped
ducts behind an aperture. The resulting structures increase
the reproducibility of commonly used simplified jet-engine
inlet models and are designed to serve as precisely-defined
radar cross section (RCS) benchmarks with reliable
reference results. The design, manufacturing, and assembly
of the measured structures are detailed; the RCS measurement setup, data collection, and post processing are
documented; and the uncertainty in measured RCS data is
quantified with the help of simulations. Results show that the
fields scattered by the structures, while highly sensitive to
geometric and material perturbations, can be both measured
and simulated accurately even at frequencies with many
propagating modes inside the pipe.
We propose a compact bistatic radar cross section
(RCS) measurement system using a new 2D plane-wave synthesis
(PWS) employing 2D propagating plane-wave expansion and a
single-cut near-field far-field transformation (SCNFFFT). Our
system has been successfully applied to the bistatic RCS
measurements of a metasurface (100 mm width, 50 mm height,
and 0.127 mm thickness) at 60 GHz where two horn antennas are
used for the PWS (Tx) and the SCNFFFT (Rx) and placed at the
circular distances of 1.735 m and 0.35 m respectively. The peak
and pattern errors of the RCS are 0.4 dB and below -25 dB
respectively. Using the proposed 2D PWS and SCNFFFT, the
compact 2D bistatic RCS measurement system is realized without
large equipment such as CATR.
Donald Hilliard, Michael Emire, Long To, October 2023
This paper presents research results conducted at the Naval Air Warfare Center Weapons Division (NAWCWD) Radar Reflectivity Laboratory (RRL) to characterize RCS measurement quality of a compact range anechoic chamber using a small resonant sphere as a test probe measured over a 3.17-octave bandwidth, which covers the first half of the resonance region. Specifically, tests were performed on 1-inch and 12-inch diameter spheres over 2-18 GHz, which is a very prevalent test spectrum for RRL customers. The spheres were tested at the quiet zone center and the 1-inch was rotationally scanned over a 1- meter radial arc within the test zone. Spectral and spatial analysis was performed using techniques developed by Dr. Dean L. Mensa [1].
Inverse Synthetic Aperture Radar (ISAR) image gating for RCS extraction using backprojection is compared with image gating using smoothed reweighted L1-optimization in this study.
The RCS of an object is measured by placing the object placed on a turntable which is rotated in an angular range while sweeping the frequency in the desired frequency range.
A common model with isotropic point scatterers fixed in the object coordinate system is used in the ISAR imaging process. This model is used to define a forward operator. The ISAR image can be formed by operating with the backpropagation operator (i.e. backprojection), the adjoint of the forward operator, on the measured RCS. This robust method to solve the inverse problem gives an image with a resolution limited by the frequency bandwidth and the angular range. The RCS for a scattering feature is commonly determined by using the forward operator on the point scatterers in the image that are determined to belong to the scattering feature in ISAR image gating.
L1-optimization is a method that can be used to get images with higher resolution and hence better separation of the different scattering features than backprojection. L1-optimization is well suited for naturally sparse ISAR images. One method to mitigate that the scatterers are restricted to a fixed grid is to use smoothed reweighting [1]. L1-optimizations are performed consecutively in a few steps where a smoothed version of the previous solution is used to determine a weighting matrix for the next step. Smoothed reweighted L1-optimization gives images with better separation of the scattering features in the ISAR image.
Simulated and measured RCS data are used to compare image gating using backprojection with gating using smoothed reweighted L1-optimization. The main conclusion of this study is that the RCS can be extracted for scattering features, not resolved in backprojection images, using the smoothed reweighted L1-optimization.
[1] D. Pinchera and M. D. Migliore, “Accurate reconstruction of the radiation of sparse sources from a small set of near-field measurements by means of a smooth-weighted norm for cluster-sparsity problems,” Electronics, vol. 10, no. 22, p. 2854, 2021.
Papa Ousmane Leye, David Martinez, Shaikha Aldhaheri, Chaouki Kasmi, Nicolas Mora, October 2022
The RCS of a target can be estimated using electromagnetic modeling if accurate geometries and material descriptions are available. An exact numerical calculation often requires prohibitive processing times. Moreover, numerical predictions with approximate techniques are difficult as it is challenging to consider all the physical phenomena. Therefore, a suitable RCS measurement facility adapted to the target size and specifications is required to estimate the RCS of a given target and to validate the numerical predictions. In general, the measurement of RCS takes place in anechoic chambers that simulate free-space and far-field conditions and where the unwanted reflections (walls, target mount, objects in the range, and the target interactions) are reduced.
This paper presents a broadband measurement and validation of the RCS of a metallic trihedral corner reflector of 30 cm sides when fully anechoic conditions are not available, and consequently, some undesirable echoes are present in the measurements. Firstly, the measurement facility calibration and the target calibration are outlined. A single target reference approach is performed using a sphere as a reference, and its scattering response is shortly described. Then, the measurement of the target is performed. After these steps, a processing procedure is applied to isolate the target response from the background and the close responses due to unwanted reflections. The post-processing technique and the acquisition system are presented and discussed. The measurements are performed at X band as a function of the viewing angle for vertical transmit and receive polarization.
To validate the technique, the RCS of the trihedral corner reflector is numerically simulated using the Integral Solver (I-Solver) of CST, with a Gaussian excitation, for vertical transmit and receive polarization. Measurements are compared with results obtained from CST software and show a good agreement with the numerical simulations. This setup will be used for RCS measurement of different complex targets and compared with measurements from other facilities to analyze and evaluate the RCS measurement uncertainty.
Shoaib Anwar, Evgueni Kaverine, Fabien Henry, Nicolas Gross, Francesco Scattone, Darko Sekuljica, Andrea Giacomini, Francesco Saccardi, Alessandro Scannavini, Per Iversen, Lars Foged, October 2022
Plane wave generator (PWG) for Over The Air (OTA) characterization of beamforming millimeter wave devices, provides an attractive solution comparing to conventional measurement techniques (Compact Antenna test Ranges (CATR) and Far-field chambers). MVG’s Plane wave generator for 5G NR FR2 applications ([1]-[4]) is an innovative tool which permits the user to measure the radiating elements with low to medium directivity radiation characteristics with excellent precision. Conventional CATR systems are not suited for stationary DUT (with / without person) measurement scenario.
In this paper, experimental results are presented for a dual-polarized PWG system, covering the 3GPP bands n257, n258 and n261 (24.25-29.5 GHz). System measurement results show good comparison with simulations and measurements of the PWG alone.
Another advantage of PWG presented here, is that we can modify the size of the QZ. Results from a pre-production unit for a 15cm QZ shows amplitude variation of less than ±1 dB and achieve more precision for smaller DUT.
Measurement results from the pre-production unit with a quiet zone of up to 38cm sphere diameter, show amplitude variations of less than ±2dB. This variation is compatible with the DUT + phantom or human measurement application.
Pattern results for Antenna Under Test (AUT) with low to medium directivity (6dBi up to 17dBi) compare well with simulations and measurements from other systems. For a given AUT, the impact of different positioning mast is also evaluated. Excellent stability of patterns, when the AUT is placed at different positions inside the QZ, is observed.
These results confirm that the dual-polarized PWG system presents an attractive solution for FR2 characterization of low to medium directivity radiating elements.
Joseph Friedel, David Oyediran, David Rohde, October 2022
The mission of the Naval Surface Warfare Center, Indian Head, Maryland, EOD Department, is to utilize the latest available technology in the advancement of Explosive Ordnance Disposal (EOD) equipment and techniques. This mission includes the test and evaluation of current and developmental systems, which will be discussed in this paper. EOD exploits multiple physical phenomena in its task of ordnance detection, including chemical and electromagnetic. Electromagnetics include RF fields, light (including laser, infrared and ultraviolet), and nuclear radiation. For each phenomena, there may be several different technologies used to provide multi-mode detection capability. This study focuses on the electromagnetic subset of detection RADAR, and specifically Ground Penetrating Radar (GPR), which is distinguished by its earth surface domain and generally downward field of view. The paper will give a very brief overview of GPR theory and equipment, its use in EOD, and then will focus on the RF test and measurement of electromagnetic fields generated by GPR systems and antennas. An RF antenna/system test plan will be detailed, along with the design and development of antenna gain and radiation pattern measurement techniques. The measured data from GPR technology will be graphically displayed, analyzed and compared in terms of the potential for GPR effectiveness.
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